A common way to form images on media, such as paper, is to use a fluid-ejection device, such as an inkjet-printing device. An inkjet-printing device has a number of inkjet-printing mechanisms, such as inkjet printhead assemblies. Each inkjet printhead assembly has a number of inkjet nozzles that eject ink, such as differently colored ink, in such a way as to form a desired image on the media. Many inks are dye-based, but other inks are pigment-based, which are usually more viscous than dye-based inks.
Inkjet printhead assemblies can lose water contained within the ink through the inkjet nozzles. When too much water is lost from the ink, the viscosity of the ink can increase, and/or the ink suspension can become unstable. To ameliorate this issue, inkjet printhead assemblies are commonly capped inside and/or outside the inkjet-printing devices when they are not being used for extended periods of time.
However, when inkjet printhead assemblies are capped, insufficient vapor loss from the printhead assemblies may occur. A vapor loss rate below a certain threshold can cause particle flocculation within the ink, where the solute of the ink comes out of the solution of the ink. As a result, poor image formation quality can result when the inkjet printhead assemblies are uncapped and are used to form a desired image on media.